Polyphenylene ether has the advantages of mechanical properties, electric properties, heat resistance, low temperature properties, low water absorption and dimensional stability, and the disadvantages of molding processability and impact resistance. Therefore, the polyphenylene ether has been blended with polystyrene or high impact polystyrene, thereby solving such a problem. In such a manner, the polyphenylene ether has been extensively used in the fields of, for example, electric and electronic parts, housings of office instruments, car parts, precision machinery parts and various industrial parts. However, a polyphenylene ether resin composition comprising the polyphenylene ether and high impact polystyrene has a disadvantage of poor chemical resistance in spite of improved impact resistance.
Therefore, there have been extensively developed various polymer alloy obtained by melt-blending the polyphenylene ether with a thermoplastic resin other than the styrenic resin. As a result, polymer allay wherein the thermoplastic resin serves as a matrix and the polyphenylene ether serves as a dispersed phase, and polymer alloy wherein the polyphenylene ether serves as a matrix and the thermoplastic resin serves as a dispersed phase begin to appear on the market. Typical examples of such polymer alloy are a polyamide-polyphenylene ether resin composition, a polyester-polyphenylene ether resin composition, a polyphenylene sulfide-polyphenylene ether resin composition and a polyolefin-polyphenylene ether resin composition. It is not too much to say that a key technology for the polymer alloy formation to obtain these resin compositions includes a technology, by which two or more materials incompatible with one another can be made compatible, thereby attaining to a suitable emulsion dispersion of a dispersed phase, and a technology, by which mechanical strength, particularly impact resistance can be given. Particularly, with respect to the latter to give impact resistance, as the usual way in a conventional polymer alloy formation, it is known that an elastomer component is blended. In many cases, a vinyl aromatic compound-conjugated diene compound block copolymer, and its hydrogenated product, namely a hydrogenated block copolymer have been used.
However, the polyphenylene ether and these block copolymers are incompatible with each other. In order to obtain compatibility, it is important that a content of the vinyl aromatic compound in the block copolymer is increased. Under the present condition, the block copolymer increased in a content of the vinyl aromatic compound cannot give a preferred impact resistance. On the other hand, when the block copolymer decreased in a content of the vinyl aromatic compound because of the impact resistance to be given is blended with the polyphenylene ether, the resulting resin composition exhibits a layer separation phenomenon because of poor compatibility between both polymers. Under the present condition, there is left a problem that such a phenomenon causes remarkable decrease of weld tensile strength.
Among thermoplastic resins constituting these polymer alloy, it is known that a polyolefin resin of a general-purpose resin, particularly a polypropylene resin, which is inferior in its impact resistance, heat resistance and rigidity in spite of properties superior in molding processability, water resistance, oil resistance, acid resistance and alkali resistance, is used in combination with an elastomer component to improve the impact resistance, or blended with a polyphenylene ether resin, so that the polypropylene resin serves as a matrix and the polyphenylene ether resin serves as a dispersed particle, thereby obtaining a resin composition improved in heat resistance and rigidity.
Prior arts relating thereto are as follows. There is proposed a resin composition, which is improved in solvent resistance and impact resistance, and which is obtained by blending a polyphenylene ether with a polyolefin (refer to, for example, U.S. Pat. No. 3,361,851). There is also described a resin composition, which is improved in impact resistance, and which is obtained by blending a polyphenylene ether with a polyolefin and a hydrogenated block copolymer (refer to, for example, U.S. Pat. No. 4,383,082 and European Pat. Pub. No. 115712).
Further, there is proposed a resin composition, which is superior in chemical resistance and processability, and which is obtained by blending a specific hydrogenated block copolymer for the purpose of modifying the resin composition obtained from a polyolefin resin and a polyphenylene ether resin (refer to, for example, JP-A-63-113058, JP-A-63-225642, U.S. Pat. No. 4,863,997, JP-A-3-72512, JP-A-4-183748 and JP-A-5-320471).
Still further, there is proposed a process for producing a resin composition superior in balance between impact resistance and rigidity, wherein a specific manner is applied to obtain the resin composition comprising a polyolefin resin, a polyphenylene ether resin and a specific hydrogenated block copolymer (refer to, for example, JP-A-4-28739 and JP-A-4-28740).
Similarly, there is a proposal that a resin composition produced in a specific manner brings about a resin composition superior in impact resistance (refer to, for example, JP-A-7-16.6026). It is also proposed that a specific hydrogenated block copolymer is blended to modify the resin composition comprising a polyolefin resin and a polyphenylene ether resin, thereby obtaining a resin composition superior in heat resistance, impact resistance and moldability (refer to, for example, JP-A-7-165998).
In addition, there is disclosed a resin composition obtained by carrying out blending of a polyolefin resin and a polyphenylene ether resin in the presence of a rubber-like substance, subjecting the resultant to chemical modification with maleic anhydride using a radical initiator and further adding a diamine compound thereto (refer to, for example, WO91/19762). Herein, it is proposed to use a polyolefin-polyphenylene ether graft product formed from the polyolefin modified with maleic anhydride and the polyphenylene ether modified with maleic anhydride through the diamine compound as a compatibilizer.
On the other hand, the present Applicant has proposed a resin composition comprising a polyphenylene ether resin, a polyolefin resin and a specific hydrogenated block copolymer, which is superior in its compatibility, rigidity and heat resistance and also in its solvent resistance (refer to, for example, JP-A-2-225563, JP-A-3-185058, JP-A-5-70679, JP-A-5-295184, JP-A-6-9828, JP-A-6-16924, JP-A-6-57130 and JP-A-6-136202).
In many of the resin compositions mentioned above, it is the present condition that the hydrogenated block copolymer is used as a compatibilizer because the polyolefin resin and the polyphenylene ether resin are naturally incompatible with each other. The compatibility of the hydrogenated block copolymer serving as the compatibilizer exhibited to the polyolefin, particularly a polypropylene resin, depends upon a kind of a conjugated diene compound used for obtaining the block copolymer prior to the hydrogenation and a vinyl bond state of the conjugated diene compound before the hydrogenation of the soft segment portion in the hydrogenated block copolymer (namely, 1,2-vinyl bond content and 3,4-vinyl bond content). The compatibility exhibited to the polypropylene resin can be remarkably improved with increase in these vinyl bond contents. However, with improvement of the compatibility, a grass transition temperature of a soft segment portion of the hydrogenated block copolymer shifts to a higher temperature side, and as a result, impact strength at low temperature required for the resin composition remarkably deteriorates. Therefore, it is the present condition that the vinyl bond state of the conjugated diene compound before the hydrogenation to obtain the hydrogenated block copolymer, which serves as both the compatibilizer and an impact resistance-imparting agent, is determined in design of a polymer with detriment to any performance (impact strength at low temperature or compatibility). Furthermore, The compatibility of the hydrogenated block copolymer serving as the compatibilizer exhibited to the polyphenylene ether resin depends upon a content of the vinyl aromatic compound in the hydrogenated block copolymer and a molecular weight of the vinyl aromatic compound polymer constituting a hard segment block. It is known that the both can be increased with remarkable improvement of the compatibility exhibited to the polyphenylene ether resin. However, under the present condition, it is not desirable for improving the impact resistance. As mentioned above, with respect to the hydrogenated block copolymer used as the compatibilizer to the polypropylene resin and the polyphenylene ether resin, there is a complex relation of antinomy as to the bond state of the conjugated diene compound before the hydrogenation of the soft segment portion in the hydrogenated block copolymer and the vinyl aromatic compound content in the hard segment portion therein for satisfying the compatibility exhibited to both resins and the impact resistance of the obtained resin composition. It is the present condition that no hydrogenated block copolymer satisfying both performances exists in the world.